1. Technical Field
The present invention relates to a satellite signal receiving device that determines the current position and adjusts the time based on signals received from positioning information satellites such as GPS satellites, to a satellite signal receiving method, and to an electronic device.
2. Related Art
Electronic devices that receive satellite signals from GPS (Global Positioning System) satellites and perform positioning and time adjustment operations are known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2008-39565.
When the electronic device is a device, such as a wristwatch, that moves with the user, the electronic device could conceivably move to an environment where satellite signals cannot be received, such as indoors or an underground mall.
If the reception process is executed in such an environment where satellite signals cannot be received, power is wasted. Reducing current consumption and avoiding wasteful reception processes are particularly important in battery-powered electronic devices such as wristwatches to assure sufficient duration time and reduce the battery size.
JP-A-2008-39565 therefore describes providing a solar panel in the electronic device, determining if the electronic device is outdoors by comparing the power output of the solar panel with a threshold value for determining if the electronic device is indoors or outdoors, and performing the reception process if determined to be outdoors.
However, solar panel power output corresponds to the illuminance of the light incident to the solar panel. It was therefore thought that an indoor/outdoor determination could be made by obtaining the power output corresponding to the illuminance when the electronic device is outdoors during the day and the illuminance when indoors, and setting the threshold value to differentiate between these power output levels.
However, even if the electronic device is outdoors, power output may not exceed the threshold value depending on the operating conditions of the electronic device. For example, when the electronic device having the satellite signal receiving device is a wristwatch, power output may not exceed the threshold value even though the electronic device is outdoors if the solar cell is covered by a sleeve, for example. Depending upon the season or the weather, power output may also not exceed the threshold value even though the electronic device is outdoors because direct sunlight is not incident or is weak.